The South Bay has rapidly developed a presence in all of these, particularly in solar (which shares technologies with semiconductor manufacture). Joint Venture Silicon Valley recently put out a Greenprint for the Valley [pdf] setting out ‘climate prosperity’ – growing a new generation of innovative, world-beating firms and dealing with climate change on the side. For solar, the upper level jobs target is 20,000 positions by 2017.

And yet … this may not turn out to be the world’s eco-region. As GBN analyst Olaf Groth told me, the sheer diversity of ‘the green economy’ presents challenges – much of has limited ICT crossover. Geographies of innovation, production and sales are diverse, and don’t really favour a single hot location. There are dozens of distinct cleantech clusters in the US and around the world; production is often outsourced; consumer markets are very localised. It will be hard for Valley firms to access all of these.

So the Valley’s traditional advantages may be of limited help. And as Karen Chapple and Bill Lester argue in forthcoming research, green industry may not mean local green jobs. The South Bay already has a number of defunct semi-conductor factories, as production shifts to cheaper locations offshore.

What can we Brits learn from this? I think there’s a few key points here. First, ‘green growth’ is feasible. But UK policymakers need to get clearer on which bits can generate growth and jobs. In energy, that means wind and tidal power; and there will be significant waste, construction, transport and maintenance markets in urban areas.

The Silicon Valley story tells us there is unlikely to be a single winner in the green economy. But it also suggests that the UK can do a lot more to push forward its own distinct eco-sectors, and develop greener cities (and valleys) while we’re doing it.